Process for the production of detergent tablets by microwave and hot air treatment

ABSTRACT

A process for producing detergent tablets by exposing a detergent composition to microwave radiation in the frequency range from 3 to 300,000 MHz while treating the detergent composition with hot air having a temperature of 50° C. to 300° C.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a process for the production of detergenttablets by microwave and hot air treatment.

The disadvantage of conventional detergent tablets which are normallyproduced by compression molding or fusion is that they do not dissolvesufficiently quickly on account of their compactness so that the activesubstances are released too slowly. In addition, the rate at which suchtablets disintegrate is too low.

2. Discussion of Related Art

Earlier hitherto unpublished International patent applicationPCT/EP94/01330 now WO 94/25563, to the disclosure of which reference isexpressly made, describes in detail the production of washing- andcleaning-active tablets using microwaves which have an extremely highdissolving or disintegrating rate coupled with high breaking strength. Acrucial requirement for the production of tablets from powder-form orgranular raw materials using microwaves is that the starting materialsshould be at least partly present in hydrated form, "hydrated" meaning"hydrated under certain conditions in regard to temperature, pressure orrelative atmospheric humidity to which the raw material is exposed orwith which the raw material is in equilibrium". The term "hydrated" isalso defined in PCT/EP94/01330. In general, hydrated starting materialsare those which contain bound water of crystallization or which arecapable of binding externally added water at least partly as water ofcrystallization or even those substances which do not form definedhydrates, but which are capable of binding water, for example alkalimetal hydroxides.

The expression "microwaves" in the context of the present invention isunderstood to cover the entire frequency range from 3 to 300,000 MHz,i.e. the frequency range which, in addition to the actual microwaverange above 300 MHz, also encompasses the radio wave range from 3 to 300MHz. This technique can be used to produce so-called macrosolids which,besides tablets, also include blocks for example. To this end, thecompounds are joined together at their points of contact with oneanother by local microwave-induced melting/sintering. The voids presentbetween the individual components of the compounds before exposure tomicrowaves provide the tablets formed with high porosity and thuscontribute towards improving the dissolving properties of the tablets.

To facilitate local sintering of the various components of thecompounds, at least some of the components must be capable of sinteringat their surface. To this end, the components of the compoundsthemselves or their surfaces must contain sufficient water so that thecomponents of the compounds melt at their points of contact when thewater is heated. According to the teaching of International patentapplication PCT/EP94/01330, the mixture to be exposed to microwaves mustbe at least partly present in hydrated form.

In the context of the present invention, therefore, the term "tablets"is not confined to any particular three-dimensional form. In principle,the tablets may assume any three-dimensional form, depending on theshape which the powder-form or granular compounds are made to assume.

The chemical composition of the generally powder-form or granularcompounds--and hence the tablets--can be varied over a very broad range,cf. the disclosure of PCT/EP94/01330.

It has now been found that tablets produced by the microwave treatmentof powder-form or granular compounds on the one hand lack the breakingstrength required for storage and transport if the microwave treatmentis too short and, on the other hand, undergo core carbonization if themicrowave treatment is too long. Hitherto, it has now always beenpossible to solve this problem because, in many cases, adequate breakingstrength inevitably involved carbonization within the tablet and theavoidance of carbonization resulted in inadequate breaking strength.

Accordingly, the problem addressed by the present invention was to finda process in which the disadvantages mentioned above would not arise,i.e. which would give tablets combining a high breaking strength withthe absence of any carbonization.

DESCRIPTION OF THE INVENTION

According to the present invention, the solution to this problem ischaracterized in that, during its exposure to microwaves, the compoundis treated with hot air at a temperature of 50° C. to 300° C.,preferably 100° C. to 250° C. and, more preferably, 150° C. to 220° C.

In the context of the invention, the expression "compound" applies tothe powder-form and/or granular mixture of detergent ingredients.Suitable detergent ingredients are, in principle, any of the substanceswhich are normally used for the production of solid cleaningformulations for textiles and hard surfaces, cf. in particular thesubstances disclosed in PCT/EP94/01330.

Suitable builders are, for example, amorphous silicates, such asmetasilicates or waterglasses, phosphates, alkali metal carbonates,alkali metal sulfates, zeolites and also organic components, such aswater-containing citrates, for example sodium citrate dihydrate, orwater-containing acetates, for example sodium acetate trihydrate.Suitable substitutes or partial substitutes for phosphates and zeolitesare crystalline layer-form sodium silicates with the general formulaNaMSi_(x) O_(2x+1).yH₂ O, where M is sodium or hydrogen, x is a numberof 1.9 to 4 and y is a number of 0 to 20, preferred values for x being2, 3 or 4. Corresponding crystalline layer silicates are described, forexample, in European patent application EP-A-0 164 514. Preferredcrystalline layer silicates are those in which M is sodium and x assumesthe value 2 or 3. Both β- and γ-sodium disilicates Na₂ Si₂ O₅.yH₂ O areparticularly preferred.

Useful organic builders are, for example, the polycarboxylic acidspreferably used in the form of their sodium salts, such as citric acid,adipic acid, succinic acid, glutaric acid, tartaric acid, sugar acids,aminocarboxylic acids, nitrilotriacetic acid (NTA), providing its use isnot objectionable on ecological grounds, and mixtures thereof. Preferredsalts are the salts of the polycarboxylic acids, such as citric acid,adipic acid, succinic acid, glutaric acid, tartaric acid, sugar acidsand mixtures thereof.

Suitable polymeric polycarboxylates are, for example, the sodium saltsof polyacrylic acid or polymethacrylic acid, for example those having arelative molecular weight of 800 to 150,000 (based on acid). Suitablecopolymeric polycarboxylates are, in particular, those of acrylic acidwith methacrylic acid and those of acrylic acid or methacrylic acid withmaleic acid. Copolymers of acrylic acid with maleic acid containing 50to 90% by weight of acrylic acid and 50 to 10% by weight of maleic acidhave proved to be particularly suitable. Their relative molecularweight, based on free acids, is generally in the range from 5,000 to200,000, preferably in the range from 10,000 to 120,000 and morepreferably in the range from 50,000 to 100,000. Biodegradableterpolymers are also particularly preferred, for example thosecontaining salts of acrylic acid and maleic acid and also vinyl alcoholor vinyl alcohol derivatives as monomers (P 43 00 772.4) or thosecontaining salts of acrylic acid and 2-alkyl allyl sulfonic acid andalso sugar derivatives as monomers (DE 42 21 381).

Other suitable builder systems are oxidation products ofcarboxy-functional polyglucosans and/or water-soluble salts thereofwhich are described, for example, in International patent applicationWO-A-93/08251 or of which the production is described, for example, inInternational patent application WO-A-93/16110.

Other preferred builders are the known polyaspartic acids and salts andderivatives thereof.

Other suitable builders are polyacetals which may be obtained byreaction of dialdehydes with polyolcarboxylic acids containing 5 to 7carbon atoms and at least three hydroxyl groups, for example asdescribed in European patent application EP-A-0 280 223. Preferredpolyacetals are obtained from dialdehydes, such as glyoxal,glutaraldehyde, terephthalaldehyde and mixtures thereof, and frompolyolcarboxylic acids, such as gluconic acid and/or glucoheptonic acid.

The inorganic and/or organic builders are used in the tablets inquantities of preferably about 10 to 60% by weight and, more preferably,15 to 50% by weight.

Solid acids, for example amidosulfonic acid or phosphonic acids, areused for the production of acidic detergent tablets.

In addition, the tablets generally contain anionic, cationic, amphotericor zwitterionic surfactants, but above all the nonionic surfactantsdisclosed in PCT/EP94/01330. Nonionic surfactants, such as fatty alcoholethoxylates for example, are preferred. In addition, the tablets mayoptionally contain oxygen- or chlorine-based bleaching agents,disinfectants, for example quaternary ammonium compounds, foaminhibitors, enzymes, fillers, etc.

The microwave treatment normally lasts 15 seconds to 90 minutes,preferably 1 minute to 30 minutes and, more preferably, 1 minute to 5minutes.

In another embodiment of the invention, the tablets are treated with hotair after the microwave treatment. In principle, there are no limits tothe time interval between the microwave treatment and the hot airtreatment although the intervening period is normally at most 24 hours,preferably at most 60 minutes and, more preferably, at most 2 minutes.In principle, the hot air treatment may last for as long as the tabletis capable of withstanding the treatment without damage. For economicreasons, the duration of the hot air treatment is up to 30 minutes,preferably up to 10 minutes and, more preferably, up to 3 minutes.

In a particularly preferred embodiment of the process according to theinvention, the treatment with hot air is carried out both during andafter the microwave treatment. In this case, too, the time intervalbetween the microwave treatment and the following hot air treatment isnormally at most 24 hours, preferably at most 60 minutes and, morepreferably, at most 2 minutes. The duration of the hot air treatment isalso normally in the range mentioned above.

The hot air is generally produced by a conventional hot air blower witha controllable air temperature.

The microwave treatment may be carried out, for example, in themicrowave oven described in PCT/EP94/01330. The products thus microwavedmay then be subjected to a hot air treatment. The microwave treatmentand the hot air treatment may also be carried out simultaneously in theoven. Accordingly, the microwave treatment and/or hot air treatment maybe carried out in batches in a single unit, for example an oven, asdescribed above.

The microwave treatment (accompanied or followed by the hot airtreatment or accompanied and followed by the hot air treatment) may becarried out continuously. To this end, the compounds to be microwavedare transported on a conveyor belt through a microwave radiation zone.In addition, hot air is blown either directly into the radiation zone orinto a zone immediately adjoining the radiation zone or both into theradiation zone and into the adjoining zone.

EXAMPLES

60 g of powder-form compounds (corresponding to formulations 1 and 2below) were brought into the required shape by manual precompaction orby precompaction in a pneumatic press under a pressure of 1 to 400 N/cm²and were then optionally removed from the container. "Manualprecompaction" means that the compound introduced into a container openon top is manually compressed from above with a stamp. The pressureapplied for manual precompression is of the order of 1 to 20 N/cm².Where a pneumatic press is used, the pressure applied is of the order of200 to 400 N/cm². The manually precompressed compounds were generallymore soluble after microwaving and hot air treatment in accordance withthe invention.! The precompactates were then placed on a conveyor beltand transported through a microwave radiation zone in which they werenot subjected to any treatment with hot air.

Working conditions

    ______________________________________    Conveyor speed    47 cm per minute    Length of the microwave                      210 cm    radiation zone    Microwave source  18 microwave emitters each                      with an output of 1200 watts,                      wavelength 2450-2470 MHZ    Distance of microwave                      9 emitters at 11 cm    source from conveyor belt                      9 emitters at 4 cm    ______________________________________

These conditions are defined as "standard conditions".

    ______________________________________    Formulation 1:    aminosulfonic acid      96% by weight    octane phosphonic acid   1% by weight    C.sub.12-18 fatty alcohol ethoxylate                             1% by weight    Na.sub.2 SO.sub.4        1% by weight    H.sub.2 O                1% by weight    Formulation 2:    pentasodium triphosphate                            40% by weight    sodium metasilicate     40% by weight    sodium metasilicate pentahydrate                            10% by weight    sodium carbonate decahydrate                             5% by weight    dimethyl dioctyl ammonium chloride                             3% by weight    C.sub.12-18 fatty alcohol ethoxylate                             2% by weight    ______________________________________

To increase the output of the assembly line, both the speed of theconveyor belt and the microwave power were doubled in relation to thestandard conditions. Unfortunately, the tablets thus obtained hadunsatisfactory breaking strength. However, a reduction in the conveyorspeed resulted in carbonization within the tablets.

When the non-breakage-resistant tablets produced at twice the conveyorspeed and twice the microwave power were treated with hot air (200° C.)for 2 minutes 45 seconds after microwaving, breakage-resistant tabletswith no sign of carbonization were obtained.

When the conveyor speed and the microwave power were again doubled, theduration of the hot air treatment had to be increased to 7 minutes 20seconds to obtain breakage-resistant tablets.

What is claimed is:
 1. A microwave process for producing detergenttablets comprising precompacting a detergent composition under apressure of 1 to 400 N/cm², transporting said detergent composition on aconveyor belt through a microwave radiation zone at a conveyor speed ofat least 94 cm/minute, exposing said detergent composition to microwaveradiation in the frequency range from above 300 to 300,000 MHz andtreating said detergent composition from about 2 to 30 minutes with hotair having a temperature of 200° C. to 300° C. within 60 minutes ofexposing said composition to said microwave radiation, wherein saidmicrowave radiation has an output effective to produce break-resistanttablets without carbonization.
 2. A process as in claim 1 wherein saiddetergent composition contains at least one partially hydratedcomponent.
 3. A process as in claim 1 conducted in batch-wise manner. 4.A process as in claim 1 wherein said detergent composition comprisesamorphous silicates, crystalline silicates, phosphates, carbonates,sulfates, zeolites and organic compounds.
 5. A process as in claim 1wherein said microwave radiation is for 15 seconds to 90 minutes.